1. Field of the Invention
The present invention relates to a vacuum switch container, a vacuum switch, a method of producing the vacuum switch container and a method of producing the vacuum switch.
2. Description of the Related Art
Heretofore, for example, in producing a vacuum switch container made of ceramics and having a cylindrical shape for use in a vacuum switch, a well-known rubber-press method has been employed.
In this rubber-press method, as is illustrated in FIG. 5, ceramic powders are first provided in a cylindrical space defined between a center pin made of a metal in a columnar shape, i.e., a metal column, and a rubber mold made of rubber in a cylindrical shape, and then an upper cap and a bottom are provided such that the cylindrical space is closed. Next, the ceramic powders are pressed from around the rubber mold to form a green compact. Thereafter, the green compact, after being cut to an appropriate shape, is fired to produce a ceramic sintered body which forms the vacuum switch container.
One disadvantage of the above-described rubber-press method is that the cutting is necessary after the above-mentioned green compact is formed so as to produce the desired dimensional accuracy, thus adding to the operational steps required. Further, because the green compact must be subjected to such cutting, an attendant problem results, i.e., a significant amount of the ceramic material is necessarily wasted as a consequence.
An object of the present invention is to solve the above-described problems, and to provide a vacuum switch container, a vacuum switch, a method of producing the vacuum switch container and a method of producing the vacuum switch, all in an easy, effective manner as compared with the prior art.
According to a first aspect of the present invention, a vacuum switch container is provided which is made of ceramics and has a cylindrical shape, wherein the container has a center line average roughness Ra of 1.0 xcexcm or less and a ten-point average roughness Rz of 10.0 xcexcm or less, in an axial direction at the outer circumferential surface of the vacuum switch container.
The vacuum switch container (i.e., the fired product) is intended for use as an insulating member in a vacuum switch.
In accordance with this aspect of the present invention, excellent insulation properties are achieved, because the outer circumferential surface of the container is extremely smooth and flat, thereby inhibiting foreign matter (e.g. an electroconductive substance such as carbon or the like) from adhering thereto. More particularly, it is of advantage in relation to the insulation properties that when a grazing layer is not formed on a surface of the container, i.e., the outer circumferential surface, such inhibition of the adherence of foreign matter to the surface is still highly effective.
According to a second aspect of the present invention, a vacuum switch container is provided which is made of ceramics and which has a cylindrical shape, wherein the container has a center line average roughness Ra of 1.0 xcexcm or less and a ten-point average roughness Rz of 10.0 xcexcm or less in axial and circumferential directions of the outer circumferential surface of the vacuum switch container (the circumferential direction being the direction along the outer circumferential surface around the axis thereof).
In accordance with this second aspect of the present invention, it is of advantage that the surface roughness is small not only in the axial direction but also in the circumferential direction of the outer circumferential surface. As a result, the insulation performance of the container is high, as in the container according to the first aspect of the invention described above.
Advantageously, a glazing layer is provided on the outer circumferential surface of the vacuum switch container. Such a glazing layer on the outer circumferential surface of the vacuum switch container makes it even more difficult for dirt to adhere thereto.
In accordance with a third aspect of the invention, a vacuum switch is provided which includes the above-described vacuum switch container as an insulating member of the switch.
The vacuum switch according to the third aspect of the present invention has excellent insulation properties which result from the use of the above-described vacuum switch container as an insulating member therein.
In accordance with a fourth aspect of the present invention, a method of producing a vacuum switch container, is provided, comprising the steps of:
producing a green compact for a vacuum switch container by subjecting ceramic granulated powders to die-molding;
firing the green compact so as to produce a fired ceramic body; and
producing the vacuum switch container from the fired compact.
In accordance with the present invention, because the ceramic granulated powders are provided in a metallic die and die pressed, i.e., a green compact is formed by die-molding, a surface thereof (and in particular, the outer circumferential surface thereof is smooth and flat and the dimensional accuracy of the container is high as compared with containers produced by the conventional rubber-press method.
As a result of the foregoing, because there is no need for cutting the outer circumferential surface of the green compact to adjust the size thereof as has conventionally been done, the operational steps used in making the container can be simplified. A further advantage is that costs are reduced because, since cutting of the outer circumferential surface is not necessary, ceramics material is not wasted. Furthermore, since the outer circumferential surface is not subjected to cutting, no cutting marks are left on the outer circumferential surface, thereby further ensuring that the surface is smooth and flat.
In the method according to the fourth aspect of the invention, the green compact may be formed by:
placing the ceramic granulated powders in a cylindrical space of a metallic die formed by a center pin, an outer mold, a lower punch and an upper punch; and
pressing the ceramic granulated powders within the space.
By using such a die-molding step, a green compact can be produced which has a smooth and flat surface and high dimensional accuracy.
The die-molding step preferably includes applying pressure on the ceramic powders in the space using the lower and upper punches.
In accordance with a fifth aspect of the present invention, a method of producing a vacuum switch is provided, further comprising, after producing the vacuum switch container by the above-described method, performing the steps of:
arranging a switch member in the vacuum switch container and producing the vacuum switch therefrom.
It will be appreciated that this method is of advantage from a cost standpoint, because the vacuum switch is produced by using the above-described method of producing the vacuum switch container, i.e., a simplified production process as compared with the prior art.
Further features and advantages of the present invention will be set forth in, or apparent from, the detailed description of preferred embodiments thereof which follows.